1. Field of the Invention
This invention relates to a sheet feeding device for feeding sheets from a sheet supporting bed such as a cassette or a deck, and more particularly to a sheet feeding device in which the mounting or dismounting operation of the sheet supporting bed can be well accomplished without the sheets being wrinkled even if a rotatable member contacts the sheets held on the sheet supporting bed when the sheet supporting bed is loaded into or removed from a predetermined position in an image forming apparatus.
2. Description of the Prior Art
Sheet feeding devices have heretofore been very commonly used which are designed such that a number of sheets are contained in a cassette having an open top and the sheets are resiliently biased from the underside thereof toward the open top side and when the cassette is mounted in a copying apparatus body or the like, a paper feed roller disposed on the body side is urged against the uppermost sheet in the cassette and also the roller is driven to feed the sheets one by one to the body side.
In the sheet feeding devices of this type, the paper feed roller disposed on the body side of the copying apparatus or the like is normally urged against the uppermost sheet held relatively loosely in the cassette and therefore, even if the drive force to the paper feed roller is cut off during the non-operative condition of the apparatus, the cassette must be drawn out against a great rotational torque required for rotating the paper feed roller when the cassette is to be removed from the body for some reason or other and therefore, there is an undesirable possibility that the uppermost sheet and plural sheets adjacent thereto in the cassette are deviated from a predetermined position in the cassette or damaged.
To avoid such a danger, the sheet feeding device has unavoidably been designed such that when the cassette is to be mounted or dismounted with respect to the copying apparatus body, the cassette is mounted or dismounted in such a direction that the sheets in the cassette do not contact the paper feed roller in the body and in a predetermined position, the cassette is somewhat pivotally moved to bring the paper feed roller into contact with the sheets, or that the cassette is mounted or dismounted with the paper feed roller on the body side permitted to escape and the paper feed roller is urged against the sheets in the cassette when the cassette has been brought to the predetermined position.
However, in the case of the former design, a part of the cassette is disposed in the interior of the body and a space in which pivotal movement can occur is required near the portion in which the paper feed roller is disposed, and this means that a space directly unnecessary for copying or printing operation is required and thus, the body becomes bulky and the operation of setting the cassette unavoidably becomes cumbersome because the cassette must be set at a predetermined position after being inserted into the body. Also, in the case of the latter design, the paper feed roller is provided with a mechanism for driving the same and therefore, making these portions movable results in a complicated construction and reduced reliability, and apparently, this is not preferable.